Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$180.55	5.153%	$189.8537	$189.85	$189.85	$189.90
Purchase #2	$91.27	5.584%	$96.3665	$96.37	$96.35	$96.40
Purchase #3	$16.71	4.860%	$17.5221	$17.52	$17.50	$17.50
Purchase #4	$129.85	9.727%	$142.4805	$142.48	$142.50	$142.50
Purchase #5	$241.75	7.229%	$259.2261	$259.23	$259.25	$259.20
Purchase #6	$122.53	4.320%	$127.8233	$127.82	$127.80	$127.80
Purchase #7	$123.59	13.436%	$140.1956	$140.20	$140.20	$140.20
7 purchase totals =	$906.25		$973.4678	$973.47	$973.45	$973.50